The investigations to be done include the development of a radioimmunoassay for the group II pepsinogens and radial immunodiffusion assays for the group I and group II pepsins, the determination of fasting serum group I and group II pepsinogen levels in control subjects and in patients with a variety of gastroduodenal disorders, the determination of different stimulants of gastric secretion on serum group I and group II pepsinogen levels and on gastric secretion of group I and group II pepsin(ogen)s, and the correlation of serum group I and group II pepsinogen levels with pepsinogen phenotype and blood type.